This invention relates to telecommunication systems and, more specifically, to transporting data streams over physical links of varying bandwidth.
In telecommunication networks or systems, data is transported from one location in the network to another location in the network at various data rates. Thus, the situation may arise, at some point in the network, where the transport or data rate for an incoming data stream exceeds the capacity of a single physical link over which the data streams needs to be transported. Data streams that exceeds the capacity of a single physical link can be split into separate streams and the separate streams sent over multiple physical links; the aggregate capacity of the lower capacity lines is sufficient to carry the data stream. This approach to splitting the data or transporting a data stream over several lines is known as “inverse multiplexing”.
One type of link is a T1 link. T1 is a full-duplex system: transmitted signals are transported on one wire pair, and received signals are transported on a separate wire pair a rate of 1.544 Mbps.
As an alternative to T1 links and equipment, links can have an E1 bit streams that are transmitted at a line rate of 2.048 Mbps.
In order to transport data, the data is packaged according to a predetermined protocol. One protocol is Asynchronous Transfer Mode (ATM). In accordance with ATM protocol, the data is packaged in cells called ATM cells. In inverse multiplexing, the ATM data or cell stream is divided into frames and transported over several low capacity lines, such as the T1 links.
One application of inverse multiplexing a high rate data stream onto a low rate data line is in systems that transport ATM cells. A typical ATM cell is 53 bytes in length. Each cell includes a payload and a header. The equipment processing the ATM cell stream may insert or delete idle ATM cells into or from, respectively, each frame. A frame includes ATM cells, control protocol cells for inverse multiplexed ATM (ICP), and/or filler cells.
Once the separate streams have passed through the low capacity portion of the network, they can be combined to form the original data stream. Known systems and methods combine or multiplex the separate data streams from the lower capacity lines at a receiver and, thereby, reconstruct the original data stream.
In order to reconstruct the original data stream from the individual low capacity data streams that are received at the receiver, the sequencing or ordering of the frames and, thus, the ATM cells must be tracked. Known methods include inserting a cell into the frame, such as the ICP cell that includes sequencing information for each frame, among other information. However, insertion of this cell results in a great deal of overhead because each ICP cell typical includes 53 bytes, of which only 1 byte is typically devoted to frame sequencing information. Additionally, in order to accurately detect if an error condition exists, cyclic redundancy check (CRC) bytes and/or ICP cells of several sequentially received ICP cells are analyzed. Thus, it takes several frames and, hence, many ATM cells pass before current systems realize that an error condition existed and currently exists. Accordingly, the time take to correct or handle the error condition is greatly increased.
Therefore, what is needed is a system and method for identifying an error condition and the sequence of a data stream that is taken from a high bandwidth line and split among low bandwidth links, which have an aggregate bandwidth that is at least equal to the high bandwidth line, with minimal overhead quick recovery from error conditions.